1. Field of the Invention
The present invention relates generally to bicycle chain rings used in bicycle drive trains. More particularly, this invention relates to bicycle chain rings with ramps and other features for improved shifting performance.
2. Description of Related Art
Conventional bicycle gear systems typically include a crankset including two or three chain rings affixed to a crank arm spider and a separate simple crank arm. The crank arms of a crankset are configured to receive pedals on one end and to be affixed at the other end to a bottom bracket spindle with bearings for rotation. Conventional bicycle gear systems also typically include a rear cog set, occasionally referred to as a cassette or cluster, having one to ten gears with teeth configured to rotate a rear wheel through a hub with bearing mechanism. Conventional bicycle gear systems further include a bicycle chain that is driven by the chain rings of the crankset which, in turn, drive the cogs of the rear cog set. The gears of the bicycle may be selectively changed using shifters with control wires attached to front and rear derailleurs that move the chain from adjacent chain rings or cogs.
Conventional front derailleurs used with cranksets having two or three chain rings push the chain from one ring to the next using lateral motion. During an up-shift, for example, the chain guide of a front derailleur pushes laterally against the side of a chain until the links of the chain finally catch on a tooth of the larger adjacent chain ring and all subsequent links of the chain follow until the chain is aligned with the teeth of the larger adjacent chain ring. A down-shift is achieved by pushing laterally against the chain resting on the larger chain ring until the chain can fall down to the smaller chain ring.
This conventional method of pushing laterally against the chain with a chain guide provides adequate shifting for most purposes. However, under extreme loading, such as sprinting or out of the saddle climbing, there is a need for quicker shifting, especially up-shifting. A number of solutions have been proposed to improve shifting performance of a front derailleur.
The inventor of the present application has invented improved front derailleurs, see e.g., U.S. Pat. Nos. 6,454,671 and 7,025,698, both to Wickliffe. These prior patents approach the problem of improved shifting by changing the way a front derailleur shifts a chain from chain ring to chain ring—by using a chain guide that physically lifts up the bicycle chain during up-shifts, and pulls down the bicycle chain during down-shifts. This is in contrast to conventional front derailleurs with their predominantly lateral movement of the bicycle chain, during both up- and down-shifts.
Other approaches to improving front derailleur shifting performance have focused on redesigning bicycle chains by shaping outer chain links to more readily grab conventional teeth found on conventional chain rings. By shaping outer chain links of a bicycle chain to bow out laterally or to have chamfered or tapered inner surfaces, such chains may be able to grab chain ring teeth quicker.
Still other approaches to improving front derailleur shifting performance have focused on redesigning the chain rings themselves. For example, U.S. Pat. No. 5,078,653 to Nagano discloses a larger chain ring with selected teeth having reduced height relative to adjacent teeth, i.e., the crests of the selected teeth having been uniformly cut off to reduce height. Additionally, a short pin has been inserted into the inside of the larger chain ring just below the trimmed teeth and opposed to the smaller chain ring. The arrangement disclosed in the '653 patent, purports to facilitate quicker down-shifts by allowing the chain to disengage at the trimmed teeth and be lowered onto the teeth of a smaller chain ring via the short pin. However, there is no indication that the invention disclosed in the '653 patent improves up-shifting, especially during high loads as mentioned above.
U.S. Pat. No. 6,666,786 to Yahata discloses another improvement to down-shifting performance through the use of chamfered chain ring teeth. However, like the '653 patent, the '786 patent does not address or attempt to solve the problem of achieving improved up-shifting.
U.S. Pat. No. 5,413,534 to Nagano and U.S. Pat. No. 6,572,500 to Tetsuka are directed toward redesigning a conventional chain ring to improve up-shifting. These two patents disclose the use of pins, or a pin in combination with tooth chamfering, to improve up-shifting. However, in both patents the pin or teeth engage a given chain link at the point directly between chain link rollers. This configuration tends to be problematic because the load points of a bicycle chain are concentrated at each of the chain link rollers (bushings surrounding pins). Thus, the use of pins as disclosed in the '534 and '500 patents to Nagano and Tetsuka, respectively, may increase stress on the chain especially during high loads and, thus, could lead to increased wear and reduce longevity of the chain.
Similarly, U.S. Pat. No. 5,876,296 to Hsu et al. discloses the use of an axially oriented recess in combination with a support protrusion to aid in up-shifting. U.S. Pat. No. 5,738,603 to Schmidt et al. discloses a chain ring with pins, chamfered teeth and missing teeth to aid in shifting. However, neither of these two patents appears to solve the problem of the added stress to the chain from the “support protrusion” or the “pins”.
FIG. 30A is a diagram illustrating a conventional chain ring using two pins to aid in shifting a chain during an up-shift. The two pins 1202 lift and drop the chain 1210 onto the larger chain ring 1212 during an up-shift. The pins 1202 provide lift in the direction of arrows 1204. The set of two pins 1202 shown in FIG. 30 are generally replicated at a location 180° opposite on the chain ring 1212. So, in a given rotation of the chain ring 1212, there are only two potential shift points that can utilize the pins 1202. Additionally, the load points 1206 are distributed along the chain pivots 1208. Thus, the lift 1204 provided by pins 1202 do not match the load points 1206 of chain 1210. When down-shifting under load with such conventional chain rings, the chain 1210 often keeps engaging the teeth 1214 due to tension and the height of all the teeth 1214 not allowing a front derailleur cage (not shown) to physically move the chain 1210 past the teeth 1214. This results in slower down-shifts, especially under load.
FIG. 30B is a diagram illustrating a “see saw action”, shown at curved double headed arrows 1218, that can occur with an unstable lift point 1216 of a single pin 1201 of a conventional chain ring (not shown) lifting upon a chain 1210. FIG. 30B also illustrates that a chain 1210 is comprised of alternating sets of inner links 1220 and outer links 1222. Conventional chain ring pins 1202 can only grab an outer link 1222. Pins 1222 ordinarily do not contact an inner link 1220. Consequently, there is approximately a 50% chance the chain 1210 will grab a pin 1202 and hopefully hold on long enough to engage the teeth 1214 (FIG. 30A). As shown in FIG. 30B, conventional chain ring designs put the entire chain load on a small contact area between the pin 1202 and an outer link 1222 of the chain 1210. The chain 1210 often slips off the pin 1202. This problem is most noticeable under load and with wear to the pin 1202.
Accordingly, there still exists a need in the art for a bicycle chain ring that achieves improved shifting performance without increasing the stress on the bicycle chain, thereby addressing at least some of the shortcomings of the prior art.